We continue to study the distribution of brain neurotransmitter or drug receptors with our newly developed autoradiographic method. We report new findings on a more parsimonious explanation of the confusing escalation of multiple opiate receptor subtypes. Studies continue to support a type I, conformationally malleable, evolutionarily recent receptor that can assume many conformational states and a type II receptor rigidly locked into a delta conformation. Applications of strategies useful for studying opiate receptors have revealed, for example, that alpha-bungerotoxin receptors and cholinergic nicotinic receptors in rat brain have two uniquely separate brain distributions.